%0 Journal Article
%T Predictability of prototype flash flood events in the Western Mediterranean under uncertainties of the precursor upper-level disturbance: the HYDROPTIMET case studies
%A R. Romero
%A A. Mart¨ªn
%A V. Homar
%A S. Alonso
%A C. Ramis
%J Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD)
%D 2005
%I Copernicus Publications
%X The HYDROPTIMET case studies (9¨C10 June 2000 Catalogne, 8¨C9 September 2002 C¨¦vennes and 24¨C26 November 2002 Pi¨¦mont) appear to encompass a sort of prototype flash-flood situations in the western Mediterranean attending to the relevant synoptic and mesoscale signatures identified on the meteorological charts. In Catalogne, the convective event was driven by a low-pressure system of relatively small dimensions developed over the mediterranean coast of Spain that moved into southern France. For C¨¦vennes, the main circulation pattern was a synoptic-scale Atlantic low which induced a persistent southerly low-level jet (LLJ) over the western Mediterranean, strengthened by the Alps along its western flank, which guaranteed continuous moisture supply towards southern France where the long-lived, quasistationary convective system developed. The long Pi¨¦mont episode, very representative of the most severe alpine flash flood events, shares some similarities with the C¨¦vennes situation during its first stage in that it was controlled by a southerly moist LLJ associated with a large-scale disturbance located to the west. However, these circulation features were transient aspects and during the second half of the episode the situation was dominated by a cyclogenesis process over the Mediterranean which gave place to a mesoscale-size depression at surface that acted to force new heavy rain over the slopes of the Alps and maritime areas. That is, the Pi¨¦mont episode can be catalogued as of mixed type with regard to the responsible surface disturbance, evolving from a large-scale pattern with remote action (like C¨¦vennes) to a mesoscale pattern with local action (like Catalogne). A prominent mid-tropospheric trough or cut-off low can be identified in all events prior and during the period of heavy rain, which clearly served as the precursor agent for the onset of the flash-flood conditions and the cyclogenesis at low-levels. Being aware of the uncertainty in the representation of the upper-level disturbance and the necessity to cope with it within the operational context when attempting to issue short to mid-range numerical weather predictions of these high impact weather events, a systematic exploration of the predictability of the three selected case studies subject to uncertainties in the representation of the upper-level precursor disturbance is carried out in this paper. The study is based on an ensemble of mesoscale numerical simulations of each event with the MM5 non-hydrostatic model after perturbing in a systematic way the upper-level disturbance, in the sense of displacing slightly this disturbance upstream/downstream along the zonal direction and intensifying/weakening its amplitude. These perturbations are guided by a previous application of the MM5-adjoint model, which consistently shows high sensitivities of the dynamical control of the heavy rain to the flow configuration about the upper-level disturbance on the day before, thus confirming the prec
%U http://www.nat-hazards-earth-syst-sci.net/5/505/2005/nhess-5-505-2005.html